1. Field of the Invention
The present invention relates to an imaging device and an imaging method usable for a camera device such as a digital camera equipped with an automatic exposure control function.
2. Description of the Related Art
A conventional digital camera for recording an image picked-up by using an imaging element such as a CCD as digital data generally comprises a display unit which functions as an electronic view finder for displaying a through-image at standby time for photographing, and as an image display monitor during reproduction of a recorded image. For the display unit, a liquid crystal monitor or the like that uses a liquid crystal panel such as a low-temperature polysilicon TFT as a display element is utilized. Recently, a display unit that uses an organic electroluminescence (EL) element to enable full-color displaying has reached a level of practical application (referred to as an organic EL monitor, hereinafter). There is now a digital camera or the like on which such an organic EL monitor is mounted.
The organic EL monitor is constituted in such a manner that self-luminous emission layers of, e.g., RGB, and a transparent electrode layer are stacked, three sub pixels are arranged in the same position to constitute one pixel (picture element), and the emission layers are individually controlled for luminance by a transparent electrode to enable full-color displaying. Driving for each pixel is carried out by a passive matrix system or an active matrix system as in the case of a liquid crystal monitor. Incidentally, it is expected that use of the organic EL monitor in the digital camera will expand because of small power consumption, possibility of thinning, no problem of an angle of a visual field which occurs in the liquid crystal monitor, and the like.
On the other hand, the digital camera or the like usually comprises an automatic exposure (AE) control function, i.e., a function of controlling a luminance level of an image signal output from an imaging element such as a CCD so that the luminance level may be a proper value. The AE control is a feedback control which calculates a control value of a diaphragm amount, an exposure time, a gain or the like based on, e.g., a luminance component contained in the image signal output from the imaging element at a predetermined exposure cycle, more specifically a luminance average of all pixels in image data generated from the image signal, and adjusts the diaphragm amount, the exposure time, the gain or the like at next exposure timing based on a result of the calculation. The control value varies from one imaging device to another. For example, in a camera of no diaphragm Ming (diaphragm amount is fixed), a control value excluding a diaphragm amount is calculated by AE control.
In the case of executing the AE control, it is uncertain whether the surroundings are bright or dark immediately after power is turned on. Thus, at the time of starting control, a medium value in a controllable range is set as the aforementioned control value. Thereafter, control is executed based on an image signal of actual imaging.